An Improved Flyback Converter

This paper presents a modified Flyback converter able to operate with higher efficiency and smaller size, overcoming most of the conventional flyback converter drawbacks, and also keeping its low cost and simplicity. In particular, the proposed converter allows the mosfet off voltage to be reduced and clamped to the input, thus recovering the transformer leakage energy. As a consequence, the duty cycle can be extended to unity, thus reducing the voltage stress across the output rectifier, and lowering both the magnetizing inductance and the transformer bias current values. In addition, due to the auxiliary mosfet, the magnetizing current can become negative, eliminating the discontinuous conduction mode (I)CM) of the conventional Flyback and allowing a smaller magnetizing inductance to be selected. Furthermore, in comparison with the conventional Flyback, the energy is supplied to the secondary side not only from the magnetizing inductance, but also from the introduced series capacitor, lowering the transformer energy requirements. The proposed converter makes also the soft-transitions possible for both mosfets. For all these reasons, as a more efficient and smaller size approach, this topology shows better performances in high power density low-cost applications.